Will a bad coolant temp sensor keep AC from running?

mhfd112 on Fri July 11, 2014 6:28 PM

Year: 2000
Make: Chevy
Model: Monte Carlo
Engine Size: 3.4

There is no power at the compressor. System is charged with freon. All fuses and relay checked good. Light is on at the AC button. Replaced pressure switch near the accumulator with a know good one.

I was about to give up when I noticed the temp gauge isn't working.

If the coolant sensor is bad, will it prevent the compressor from running?

GM Tech on Fri July 11, 2014 7:57 PM

a/c function aborts if engine temp exceeds 255 degf

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mhfd112 on Sat July 12, 2014 10:17 AM

I checked the coolant sensor wires. Only one has voltage. I found on the internet that they are both supposed to have around 5 volts when the key is on. Guessing the problem is in the pcm.

wptski on Sat July 12, 2014 11:38 AM

Quote
Originally posted by: mhfd112
I checked the coolant sensor wires. Only one has voltage. I found on the internet that they are both supposed to have around 5 volts when the key is on. Guessing the problem is in the pcm.
It's a resistor and has B+ on one end but less on the other while connected. If you pulled the connector and checked it then, you may only have voltage on one wire. Years ago, manuals listed resistance charts at certain temperatures that one could go by.

Try back probing the connector wire with a paperclip, etc. You slide the bent up paperclip down alongside the wires but sometimes this is hit/miss.

Edited: Sat July 12, 2014 at 11:40 AM by wptski

bohica2xo on Sun July 13, 2014 7:52 PM

Coolant temp sensor is probably failed, forcing you in to limp home mode. The PCM does all sorts of things with a bad ECT sensor. No gauge means it runs rich, guessing at things from the IAT.

Buy a new sensor.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

mhfd112 on Mon July 14, 2014 11:19 PM

Just found out ETC was changed recently in attempt to fix temp gauge.

mk378 on Tue July 15, 2014 12:02 AM

Check sensor ohms and confirm not open circuit, almost all of them will be less ohms hot versus cold. Also check that the pins in the connector are making contact with the sensor.

The wire that has zero volts with sensor connected could be shorted to ground. Check with ohm meter with battery disconnected.